The invention relates to alkylidene complexes of ruthenium containing N-heterocyclic carbene ligands and a process for preparing olefins by olefin metathesis from acyclic olefins having two or more carbon atoms or/and from cyclic olefins having four or more carbon atoms using at least one of these alkylidene complexes as catalyst.
Cxe2x80x94C coupling reactions catalyzed by transition metals are among the most important reactions of organic synthetic chemistry. In this context, olefin metathesis makes a significant contribution, since this reaction enables by-product-free olefins to be synthesized. Olefin metathesis has not only a high potential in the area of preparative, organic synthesis (RCM, ethenolysis, metathesis of acyclic olefins) but also in polymer chemistry (ROMP, ADMET, alkyne polymerization). Since its discovery in the 1950s, a number of industrial processes have been able to be realized. Nevertheless, olefin metathesis has developed into a broadly applicable synthetic method only recently due to the discovery of new catalysts (J.C. Mol in: B. Cornils, W. A. Herrmann: Applied Homogeneous Catalysis with Organometallic Compounds, VCH, Weinheim, 1996, p. 318-332; M. Schuster, S. Blechert, Angew. Chem. 1997, 109, 2124-2144; Angew. Chem. Int. Ed. Engl. 1997, 36, 2036-2056).
Numerous, fundamental studies have made important contributions to the understanding of this transition metal-catalyzed reaction in which an exchange of alkylidene units between olefins occurs. The generally accepted mechanism involves metal-alkylidene complexes as active species. These react with olefins to form metallacyclobutane intermediates which undergo cycloreversion to once again form olefins and alkylidene complexes. The isolation of metathesis-active alkylidene and metallacyclobutane complexes supports these mechanistic hypotheses.
Numerous examples may be found, in particular, in the coordination chemistry of molybdenum and tungsten. Specifically the work of Schrock gave well-defined alkylidene complexes whose reactivity can be controlled (J. S. Murdzek, R. R. Schrock, Organometallics 1987, 6, 1373-1374). The introduction of a chiral ligand sphere in these complexes made possible the synthesis of polymers having a high tacticity (K. M. Totland, T. J. Boyd, G. C. Lavoie, W. M. Davis, R. R. Schrock, Macromolecules 1996, 29, 6114-6125). Chiral complexes of the same structural type have also been used successfully in ring-closing metathesis (O. Fujimura, F. J. d. L. Mata, R. H. Grubbs, Organometallics 1996, 15, 1865-1871). However, the high sensitivity toward functional groups, air and water is a drawback.
Recently, phosphine-containing complexes of ruthenium have become established (R. H. Grubbs, S. T. Nguyen, L. K. Johnson, M. A. Hillmyer, G. C. Fu, WO 96/04289, 1994; P. Schwab, M. B. France, J. W. Ziller, R. H. Grubbs, Angew. Chem., 1995, 107, 2179-2181; Angew. Chem. Int. Ed. Engl. 1995, 34, 2039-2041). Owing to the electron-rich, xe2x80x9csoftxe2x80x9d character of later transition metals, these complexes have a high tolerance toward hard, functional groups. This is demonstrated, for example, by their use in natural product chemistry (RCM of dienes) (Z. Yang, Y. He, D. Vourloumis, H. Vallberg, K. C. Nicolaou, Angew. Chem. 1997, 109, 170-172; Angew. Chem., Int. Ed. Engl. 1997, 36, 166-168; D. Meng, P. Bertinato, A. Balog, D. S. Su, T. Kamenecka, E. J. Sorensen, S. J. Danishefsky, J. Am. Chem. Soc. 1997, 119, 2733-2734; D. Schinzer, A. Limberg, A. Bauer, O. M. Bxc3x6hm, M. Cordes, Angew. Chem. 1997, 109, 543-544; Angew. Chem., Int. Ed. Engl. 1997, 36, 523-524; A. Fxc3xcrstner, K. Langemann, J. Am. Chem. Soc. 1997, 119, 9130-9136).
However, the range of variation of the phosphine ligands used is very restricted due to steric and electronic factors. Only strongly basic, bulky alkylphosphines such as tricyclohexylphosphine, triisopropylphosphine and tricyclopentylphosphine are suitable for the metathesis of acyclic olefins and relatively unstrained ring systems. Accordingly, the reactivity of these catalysts cannot be adjusted. Chiral complexes of this structural type have also not been able to be obtained.
For these reasons, it is an object of the invention to develop tailored metathesis catalysts which have a high tolerance toward functional groups as a result of a variable ligand sphere and which allow fine adjustment of the catalyst for specific properties of different olefins.
This object is achieved according to the invention by a complex of ruthenium of the structural formula I, 
where X1 and X2 are identical or different and are each an anionic ligand,
R1 and R2 are identical or different and can also contain a ring, and R1 and R2 are each hydrogen or/and a hydrocarbon group, where the hydrocarbon groups are identical or different and are selected independently from among straight-chain, branched, cyclic or/and noncyclic radicals from the group consisting of alkyl radicals having from 1 to 50 carbon atoms, alkenyl radicals having from 1 to 50 carbon atoms, alkynyl radicals having from 1 to 50 carbon atoms, aryl radicals having from 1 to 30 carbon atoms and silyl radicals,
where one or more of the hydrogen atoms in the hydrocarbon or/and silyl groups can be replaced independently by identical or different alkyl, aryl, alkenyl, alkynyl, metallocenyl, halogen, nitro, nitroso, hydroxy, alkoxy, aryloxy, amino, amido, carboxyl, carbonyl, thio or/and sulfonyl groups,
the ligand L1 is an N-heterocyclic carbene of the formulae II-V and the ligand L2 is an uncharged electron donor, in particular an N-heterocyclic carbene of the formulae II-V or an amine, imine, phosphine, phosphite, stibine, arsine, carbonyl compound, carboxyl compound, nitrile, alcohol, ether, thiol or thioether, 
where R1, R2, R3 and R4 in the formulae II, III, IV and V are identical or different and are each hydrogen or/and a hydrocarbon group,
where the hydrocarbon groups comprise identical or different, cyclic, noncyclic, straight-chain or/and branched radicals selected from the group consisting of alkyl radicals having from 1 to 50 carbon atoms, alkenyl radicals having from 1 to 50 carbon atoms, alkynyl radicals having from 1 to 50 carbon atoms and aryl radicals having from 1 to 30 carbon atoms, in which at least one hydrogen may be replaced by functional groups, and where one or both of R3 and R4 may be identical or different halogen, nitro, nitroso, alkoxy, aryloxy, amido, carboxyl, carbonyl, thio or/and sulfonyl groups.
The alkyl radicals, alkenyl radicals or alkynyl radicals in the formulae I to V preferably have from 1 to 20 carbon atoms, particularly preferably from 1 to 12 carbon atoms.
The complexes of the invention are highly active catalysts for olefin metathesis. They are particularly inexpensive. In olefin metathesis, the catalysts of the invention display not only a high tolerance toward a variety of functional groups but also a wide range of possible variations in the ligand sphere. Variation of the preparatively readily obtainable N-heterocyclic carbene ligands enables activity and selectivity to be controlled in a targeted manner and, in addition, chirality can be introduced in a simple way.
The anionic ligands X1 and X2 of the complex of the invention, which are identical or different, are preferably each halide, pseudohalide, tetraphenylborate, perhalogenated tetraphenylborate, tetrahaloborate, hexahalophosphate, hexahaloantimonate, trihalomethanesulfonate, alkoxide, carboxylate, tetrahaloaluminate, tetracarbonylcobaltate, hexahaloferrate(III), tetrahaloferrate(III) or/and tetrahalopalladate(II), with preference being given to halide, pseudohalide, tetraphenylborate, perfluorinated tetraphenylborate, tetrafluoroborate, hexafluorophosphate, hexafluoroantimonate, trifluoromethanesulfonate, alkoxide, carboxylate, tetrachloroaluminate, tetracarbonylcobaltate, hexafluoroferrate(III), tetrachloroferrate(III) or/and tetrachloropalladate(II) and preferred pseudohalides being cyanide, thiocyanate, cyanate, isocyanate and isothiocyanate.
In the formulae II, III, IV and V, some or all of the hydrogen in the hydrocarbon groups R1, R2, R3 and R4 can be replaced independently by identical or different halogen, nitro, nitroso, hydroxy, alkoxy, aryloxy, amino, amido, carboxyl, carbonyl, thio, sulfonyl or/and metallocenyl groups. In these formulae, R3 and R4 can form a fused-on ring system.
The ligands L1 and L2 of the complex of the structural formula I can form a chelating ligand of the formula VI 
where the bridges Y can comprise cyclic, noncyclic, straight-chain or/and branched radicals selected from the group consisting of alkylene radicals having from 1 to 50 carbon atoms, alkenylene radicals having from 1 to 50 carbon atoms, alkynylene radicals having from 1 to 50 carbon atoms, arylene radicals having from 1 to 30 carbon atoms, metallocenylene, borylene and silylene radicals in which one or more hydrogens may be replaced independently by identical or different alkyl, aryl, alkenyl, alkynyl, metallocenyl, halo, nitro, nitroso, hydroxy, alkoxy, aryloxy, amino, amido, carboxyl, carbonyl, thio or/and sulfonyl groups, preferably alkyl, aryl or/and metallocenyl groups.
The ligands of the formulae II, III, IV, V or/and VI can have central, axial or/and planar chirality.
In the structural formula I of the complex, R1 and R2 are preferably, hydrogen, substituted or/and unsubstituted alkyl, alkenyl or/and aryl radicals, X1 and X2 are preferably halide, alkoxide or/and carboxylate ions and L1 and L2 are preferably each an N-heterocyclic carbene of the formula II.
The complexes are usually synthesized by ligand replacement in corresponding phosphine complexes. Two phosphine ligands can be replaced selectively in accordance with the reaction equation (1) or only one can be replaced in accordance with reaction equation (2). In the case of single replacement, the second phosphine can be replaced selectively by another electron donor, e.g. pyridine, phosphine, N-heterocyclic carbene, phosphite, stibene, arsine, in accordance with reaction equation (3).
In particular, this route makes it possible for the first time to prepare chiral, metathesis-active catalysts based on ruthenium (example complexes 2 and 3). 
The complexes of the invention are found to be extremely efficient catalysts in olefin metathesis. The excellent metathesis activity is demonstrated in the examples by means of a number of examples of different metathesis reactions.
The present invention therefore also encompasses processes for all olefin metathesis reactions such as ring-opening metathesis polymerization (ROMP), metathesis of acyclic olefins, ethenolysis, ring-closing metathesis (RCM), acyclic diene metathesis polymerization (ADMET) and depolymerization of olefin polymers. The high stability and tolerance of the complexes of the invention toward functional groups, in particular alcohol, amine, thiol, ketone, aldehyde, carboxylic acid, ester, amide, ether, silane, sulfide and halogen groups, makes it possible for such functional groups to be present during the metathesis reaction.
The object of the invention is also achieved by a process for preparing acyclic olefins having two or more carbon atoms or/and cyclic olefins having four or more carbon atoms, in each case of the formula VII 
from acyclic olefins having two or more carbon atoms or/and from cyclic olefins having four or more carbon atoms, in each case corresponding to the formula VII by an olefin metathesis reaction in the presence of at least one catalyst, wherein
a catalyst as claimed in any one of claims 1 to 7 is used and Rxe2x80x21, Rxe2x80x22, Rxe2x80x23 and Rxe2x80x24 in the formula VII are hydrogen or/and hydrocarbon groups,
where the hydrocarbon group is each selected independently from among straight-chain, branched, cyclic or/and noncyclic radicals of the group consisting of alkyl radicals having from 1 to 50 carbon atoms, alkenyl radicals having from 1 to 50 carbon atoms, alkynyl radicals having from 1 to 50 carbon atoms, aryl radicals having from 1 to 30 carbon atoms, metallocenyl or/and silyl radicals, in which one or more hydrogens may be replaced by a functional group,
where one or more of Rxe2x80x21, Rxe2x80x22, Rxe2x80x23 and Rxe2x80x24 may independently be identical or different halogen, nitro, nitroso, hydroxy, alkoxy, aryloxy, amino, amido, carboxyl, carbonyl, thio, sulfonyl or/and metallocenyl groups.
The olefins used preferably contain one or more double bonds. In particular, Rxe2x80x21, Rxe2x80x22, Rxe2x80x23 and Rxe2x80x24 in the olefins of the formula VII to be prepared form, in pairs, one or more identical or different rings.
Preferably, some or all of the hydrogen atoms in the hydrocarbon groups Rxe2x80x21, Rxe2x80x22, Rxe2x80x23 and Rxe2x80x24 of the olefins of the formula VII to be prepared are replaced independently by identical or different halogen, silyl, nitro, nitroso, hydroxy, alkoxy, aryloxy, amino, amido, carboxyl, carbonyl, thio, sulfonyl or/and metallocenyl groups.
The process of the invention can be carried out in the presence or absence of solvents, but preferably in the presence of organic solvents. The process of the invention can advantageously be carried out with addition of a Brxc3x6nsted acid, preferably HCl, HBr, HI, HBF4, HPF6 or/and trifluoroacetic acid, or/and with addition of a Lewis acid, preferably BF3, AlCl3 or/and ZnI2.
Surprisingly, this makes it possible for the first time to tailor a wide variety of olefins individually to different properties on the basis of small variations in the catalysis conditions or/and the catalysts, since the process of the invention for preparing olefins has an unexpectedly high tolerance toward functional groups.